Electrically heated windshields are being introduced in the U.S. automotive market. These windshields find particular utility as the forward vision unit for automobiles. Since such windshields are heated by the electrical system of the motor vehicle, the defogging and deicing of the windshield may be accomplished as soon as the key is turned on in the vehicle to actuate the electrical system thereof. There is no waiting for the engine to heat a fluid so that heat may be derived from the fluid in the normal heating and defrosting mode of the heater. The heating is accomplished by flowing electrical energy from one bus bar to another bus bar through a conductive coating that is formed as part of the windshield. The conductive coating, of course, has to be substantially transparent so that the unit may serve as a vision unit.
The particular improvement of my invention is the manner in which a part of the electrically heated windshield assembly is formed as will become more apparent from the description set forth hereinbelow.
A search was carried out on the subject matter of this disclosure in the U.S. Patent and Trademark Office. As a result of that search, the following U.S. patents were cited: U.S. Pat. Nos. 2,761,945; 3,063,881; 3,532,858; and 4,385,226. I will discuss each of these patents briefly below.
U.S. Pat. No. 2,761,945, issued on Sept. 4, 1956, for a "Light Transmissive Electrically Conducting Article." This patent discloses an electrically conductive, light transmissive article. The article includes a transparent support body and a light transparent metal film permanently adhered to one entire surface of the support body. A relatively hard transparent protective coating covers the metal film and terminates inwardly of opposed marginal areas of that film. A highly electrically conductive material is applied as an electrode over the exposed marginal edge areas of the metal film in direct contact therewith. The electrically conductive material overlaps a portion of the protective coating.
U.S. Pat. No. 3,063,881, issued on Nov. 13, 1962, for a "Method of Making an Electrically Conductive Article." This patent discloses a method of uniformly increasing the overall resistance of a transparent electrically conductive article without altering the optical characteristics thereof. The method disclosed is one wherein a transparent electrically conductive film having a protective coating thereon covers over an entire surface of a transparent support body. A pair of spaced electrodes are provided which cover the film along oppositely disposed edges of the support body so as to supply electrical current to the film. The method of this patent is one which comprises masking at least one of the electrodes along a substantially straight line extending the entire length of the electrode and thereafter removing that portion of the electrode which lies between the line and the inner edge of the electrode. In this manner the distance through which the current passes is increased as it flows between the electrodes. Thereafter, a protective coating is placed over the surface of the exposed film.
U.S. Pat. No. 3,532,858, issued on Oct. 6, 1970, for a "Thermal Window." This patent discloses a thermal window which is of the following construction. A mounting gasket is provided of resilient, rubbery dielectric material having a channel therein extending along its longitudinal dimension. This channel defines spaced side walls. A pane of glass, having an edge fitting the channel, is also provided. A thermal grid, including a plurality of electrical conductor strips, extends in spaced relation permitting visibility through the pane. These thermal strips generally extend in spaced relationship in a direction generally transverse of the channel. A bus bar electrically connects the ends of the strips and is interposed between the pane and one side wall of the channel. The bus bar has an edge portion exposed to the atmosphere extending longitudinally along the gasket out of contact therewith. The edge portion is adequate in itself to carry the electrical current passing through the thermal grid.
U.S. Pat. No. 4,385,226, issued on May 24, 1983 , for an "Electrically Heated Window." This patent discloses an electrically heated windshield which achieves a more uniform current density at the interface between the resistive heating layer and the current-bearing electrodes to which it is connected. In one embodiment, the more uniform current density connection is achieved by forming the edge of the electrode in an undulating shape. The connection may also be made by increasing the surface resistance of the electrode near its edge by, for example, forming the edge so that it is wedge-shaped in cross-section. More uniform current density may also be achieved by using an electrode which has a resistivity that is greater than that of the resistive heating layer. It may also be achieved by use of a high resistivity layer located between the electrode and the resistive heating layer.
It is my opinion that none of the prior art cited in the search report carried out on the subject matter of this specification anticipates my method for making part of an electrically heated windshield assembly. These patents are devoid of teaching or any suggestion of the method of my invention as will become readily apparent upon further reading of this specification.